この論理式は充足可能ですか？

前提・状況

(x1 | x2 | x3 | x4) &
(x5 | x6 | x7 | x8) &
(x9 | x10 | x11 | x12) &
(x13 | x14 | x15 | x16) &
(x17 | x18 | x19 | x20) &

(!x1 | !x5) &
(!x1 | !x9) &
(!x1 | !x13) &
(!x1 | !x17) &
(!x5 | !x9) &
(!x5 | !x13) &
(!x5 | !x17) &
(!x9 | !x13) &
(!x9 | !x17) &
(!x13 | !x17) &

(!x2 | !x6) &
(!x2 | !x10) &
(!x2 | !x14) &
(!x2 | !x18) &
(!x6 | !x10) &
(!x6 | !x14) &
(!x6 | !x18) &
(!x10 | !x14) &
(!x10 | !x18) &
(!x14 | !x18) &

(!x3 | !x7) &
(!x3 | !x11) &
(!x3 | !x15) &
(!x3 | !x19) &
(!x7 | !x11) &
(!x7 | !x15) &
(!x7 | !x19) &
(!x11 | !x15) &
(!x11 | !x19) &
(!x15 | !x19) &

(!x4 | !x8) &
(!x4 | !x12) &
(!x4 | !x16) &
(!x4 | !x20) &
(!x8 | !x12) &
(!x8 | !x16) &
(!x8 | !x20) &
(!x12 | !x16) &
(!x12 | !x20) &
(!x16 | !x20)